Damage of supercoiled DNA by an ultrafast laser-driven electron x-ray source.

Using magnetic fields to differentiate the effects of electrons and x-rays, it was discovered that single strand breaks in supercoiled DNA were mainly caused by the energetic ultrafast electrons rather than the ultrafast x-ray photons emitted from the same table-top ultrafast x-ray source. At constant pulse energy of the driving laser pulses, shorter laser pulses produced more strand breaks than longer ones. This was attributed to the increased flux of electrons produced with the shorter laser pulses. Other factors contributing to the DNA damage were investigated and discussed.